The present invention relates generally to combustion of hydrocarbon fuel and, more particularly, to a combustion engine that extracts hydrogen from exhaust fluid for recirculation through an exhaust turbine. The combustion engine is further configured to combust an oxygen-enriched fraction of air with the hydrocarbon fuel in a manner such that the production of nitrous oxide (NOx) and carbon dioxide (CO2) emissions in the exhaust is reduced or eliminated.
In the operation of a typical combustion engine, heat energy is converted to mechanical energy in order to provide power for transportation, to produce electricity or to operate machinery. Combustion engines may operate in a cycle of repeated sequences of compressing a working fluid to a high pressure, heating the working fluid to a high temperature, then expanding the working fluid to produce mechanical work. Several different thermodynamic energy systems are commonly utilized for producing mechanical energy from heat energy.
Large-scale electric power plants use the Rankine system wherein the working fluid is a liquid such as water. The water evaporates when heated and then expands to produce mechanical work such as to turn a turbine which, when connected to a generator, produces electricity. The exhaust vapor from the turbine condenses and the water is pumped back to a boiler to repeat the cycle. Unfortunately, the large amount of heat that is lost during the condensation of the steam limits most Rankine system power plants to an efficiency of less than about 35%.
The Brayton system uses a gas, typically air, as the working fluid and may be configured as either open-cycle or closed-cycle. The gas turbine is a typical example of an open-cycle Brayton system. Air that is drawn into a compressor is heated and expanded through a turbine and exhausted into the atmosphere. The gas releases some of its heat to a heat exchanger after leaving the turbine. One disadvantage of the closed-cycle Brayton system is that a large heat exchanger is needed in order to transfer heat from an external combustion source to the working gas. However, a closed-cycle Brayton system has the advantage of using a compressed working gas which reduces equipment size and has a much lower air-to-fuel ratio than conventional open-cycle Brayton systems. Unfortunately, the consumption by the compressor of a large portion of mechanical work produced by the turbine limits the efficiency of the Brayton system to only about 40%.
Furthermore, the components required for compressing the air occupy about one-half of the total volume of the Brayton engine and account for approximately one-half of its total cost. The Otto and Diesel systems are most commonly represented by internal combustion engines commonly utilized by automobiles, trucks and ships wherein the working fluid is also a gas such as air. The internal combustion engines of the Otto and Diesel systems include complex reciprocating piston equipment for intermittently combusting hydrocarbon fuel with the air. However, such systems produce excessive noise and vibration with the additional drawback of large frictional losses occurring between the pistons and seals, thus limiting the efficiency the Otto and Diesel systems to about 40%
During the heating phase of each of the above-described thermodynamic systems, hydrocarbon fuel is combusted with air in order to raise the temperature of the working fluid. Unfortunately, exhaust fluids that are a byproduct of the combustion reaction may contain emissions that are harmful to the environment and to human health. Such emissions may take on a number of forms and may include oxides of nitrogen (NOx), carbon monoxide, (CO), carbon dioxide (CO2) and unreacted fuel in the form of particulate matter. Particulate matter is comprised mainly of unburned hydrocarbons.
The higher the inefficiency of the combustion engine, the greater the amount of unreacted fuel that is emitted from the combustion reaction and the greater the amount of fuel that is consumed per unit of power that is produced by the engine. In addition, the increase in fuel consumption also increases the cost of operating the engine. Furthermore, because the hydrocarbon fuel typically utilized in most combustion engines is comprised of non-renewable fossil fuels, poor fuel consumption has an adverse impact on the environment in that less accessible fuel sources must be extracted from ecologically sensitive locations around the world.
The United States Environmental Protection Agency (EPA) is responsible for regulating emissions that can be harmful to human health. The EPA designates the set of harmful emissions as criteria pollutants. Included in the set of criteria pollutants are CO, NO2 and other byproducts that are exhausted from the above-mentioned thermodynamic systems. Exposure to high levels of CO is associated with visual impairment in humans. NO2 can irritate the lungs and lower resistance to respiratory infections. NO2 is also an ingredient of acid rain which can damage trees and lakes. Although naturally occurring to some degree in the atmosphere, increased concentrations of NO2 and CO2 as byproducts of fossil fuel combustion can lead to an increase in the global average temperature, also known as global warming. These so called greenhouse gases absorb heat in the atmosphere.
Reports indicate that the continuing increase of NO2 and CO2 concentrations in the atmosphere will lead to a dangerous interference with the planet's climate system, resulting in more frequent and stronger storms, floods and droughts that may threaten food production while simultaneously increasing insect-borne disease as a hazard to human health. The severity of the problem is such that in recent years, a number of international treaties specifically aimed at reducing the emission of greenhouse gases have been ratified by developing countries. Furthermore, individual nations have developed a wide variety of programs specifically targeted at reducing the level of environmentally harmful emissions.
The prior art approaches to addressing the above-mentioned emissions problems are numerous. One such approach to reducing emissions is by the after-treatment of exhaust in order to reduce the amount of unreacted hydrocarbons. In this approach, air is introduced into the high temperature exhaust stream in order to continue oxidizing unburned hydrocarbons. While this method is effective in eliminating harmful emissions, the overall efficiency of the engine is not improved. Furthermore, after-treatment of exhaust requires additional emissions control components that add weight and complexity to the combustion engine as they must be configured to withstand the increased temperatures occurring within the exhaust stream.
Another drawback to this approach is the injection of air into the exhaust stream results in an increase in NOx production. This occurs because in a high temperature exhaust, nitrogen will mix with excess oxygen that is not burned in the combustion chamber. Another prior art approach to reducing emissions is to inject atomic nitrogen into the exhaust stream which causes oxides of nitrogen (NOx) to be reduced to nitrogen and oxygen. A common source of atomic nitrogen is ammonia (NH3). However, storing and/or transporting NH3 near a power plant or in an automobile is not practical from both a complexity and operational standpoint nor is it cost effective.
As can be seen, there exists a need to provide a combustion engine that reduces or eliminates that production of environmentally harmful and hazardous greenhouse gases such as NOx, CO2 and VOC's. There also exists a need for a simple combustion engine requiring no emissions control equipment such that the overall cost and complexity of the combustion engine may be reduced. In addition, there exists a need for a combustion engine that may operate without a large heat exchanger that is typically required of closed-cycle Brayton systems. Furthermore, there exists a need for a combustion engine with a high operating efficiency and low fuel consumption. Additionally, there exists a need for a combustion engine having the capability of capturing CO2 as an aid in global warming abatement.